With ever increasing recording density of magnetic recording media, the surfaces of the magnetic recording media need to be flat to enable the recording head to float closely over the surface. To improve the magnetic recording media, a variety of proposals have been made with regard to the composition and structure of magnetic layers, materials for non-magnetic underlayer, materials for non-magnetic substrates, and so forth. Aluminum and glass are mainly used as material for the non-magnetic substrates, but plastic materials, in particular high polymer resin material, have been proposed as materials for the non-magnetic substrates based on their characteristics.
It is desirable for the high recording density magnetic recording media to have long-term reliability, even for use in the severe environment, to enable a low floating magnetic head to maximize a higher recording density, and for digital electric home appliances that are expected to be widely used in the near future. An extremely low temperature of −40° C. to a high temperature and high humidity of 80° C./80% RH are assumed as the severe conditions, and under such conditions, the future magnetic recording media need to be durable, such as being operable without any problem for five years. Further, the cost of the magnetic recording media for use with the digital electric home appliances needs to be considerably lower than that of the conventional magnetic recording media. Magnetic recording media using plastic substrates have a future, but they need to be improved for use with severe conditions. That is, if a conventional magnetic recording medium using a plastic substrate is subjected to severe conditions, film expansion, i.e., a kind of film exfoliation, can occur.
There is a need for a magnetic recording medium, which uses a plastic substrate, that overcomes the film expansion problem. The present invention addresses this need.